Hi Carlo, On 29/01/2024 18:17, Carlo Nonato wrote: > > > Shared caches in multi-core CPU architectures represent a problem for > predictability of memory access latency. This jeopardizes applicability > of many Arm platform in real-time critical and mixed-criticality > scenarios. We introduce support for cache partitioning with page > coloring, a transparent software technique that enables isolation > between domains and Xen, and thus avoids cache interference. > > When creating a domain, a simple syntax (e.g. `0-3` or `4-11`) allows > the user to define assignments of cache partitions ids, called colors, > where assigning different colors guarantees no mutual eviction on cache > will ever happen. This instructs the Xen memory allocator to provide > the i-th color assignee only with pages that maps to color i, i.e. that > are indexed in the i-th cache partition. > > The proposed implementation supports the dom0less feature. > The proposed implementation doesn't support the static-mem feature. > The solution has been tested in several scenarios, including Xilinx Zynq > MPSoCs. > > Open points: > - Michal found some problem here > https://patchew.org/Xen/20230123154735.74832-1-carlo.non...@minervasys.tech/20230123154735.74832-4-carlo.non...@minervasys.tech/#a7a06a26-ae79-402c-96a4-a1ebfe8b5...@amd.com > but I havent fully understood it. In the meantime I want to advance with v6, > so I hope we can continue the discussion here. The problem is that when LLC coloring is enabled, you use allocate_memory() for hwdom, just like for any other domain, so it will get assigned a VA range from a typical Xen guest memory map (i.e. GUEST_RAM{0,1}_{BASE,SIZE}). This can result in memory conflicts given that the HW resources are mapped 1:1 to it (MMIO, reserved memory regions). Instead, for hwdom we should use the host memory layout to prevent these conflicts. A good example is find_unallocated_memory(). You need to: - fetch available RAM, - remove reserved-memory regions, - report ranges (+aligning the base and skipping banks that are not reasonable big) This will give you a list of memory regions you can then use to pass to allocate_bank_memory(). The problem, as always, is to determine the size of the first region so that is is sufficiently large to keep kernel+dtb+initrd in relatively close proximity.
~Michal
